Turbocompressor rotor and method for producing the same

ABSTRACT

A turbocompressor rotor for a turbocompressor for compressing process gas has a rotor body which makes contact with the process gas and which is produced entirely from a stainless steel material including 0.3 to 1.2% carbon and 12 to 19% chromium, wherein the steel material includes the alloy X39CrMo17-1.9. A process for producing such a turbocompressor rotor by casting includes manufacturing a casting model corresponding to the geometry of the rotor body by rapid technology and producing a casting mold using the casting model, or manufacturing a casting mold corresponding to the negative geometry of the rotor body by rapid technology, introducing the liquid steel material into the casting mold to form a cast workpiece as the rotor body, and finishing the turbocompressor rotor with the rotor body.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the US National Stage of International Application No. PCT/EP2012/051683 filed Feb. 1, 2012, and claims benefit thereof, the entire content of which is hereby incorporated herein by reference. The International Application claims priority to German Application No. 10 2011 003 632.6 DE filed Feb. 4, 2011, the entire contents of which is hereby incorporated herein by reference.

FIELD OF INVENTION

The invention relates to a turbocompressor rotor and to a process for producing the turbocompressor rotor.

BACKGROUND OF INVENTION

Turbocompressors, in particular of axial and radial construction, are used in plant construction for compressing process gas. The process gas can be a gas mixture or a gas of a single type which is contaminated with particles. By way of example, this contamination can be caused by the fact that the turbocompressor is used as an air compressor in an air separation plant and the air flowing into the turbocompressor contains sand from the environment. Similarly, the process gas is contaminated with particles if, for example, the process gas is conducted in a closed process through a loose bed of a catalyst, as a result of which dust particles of the catalyst are entrained by the process gas.

For compressing the process gas, the turbocompressor has at least one turbocompressor rotor, which is usually rotated by a drive assembly mounted on a shaft. The turbocompressor rotor has a rotor body, which is formed by blades which, when they rotate, transfer force to the process gas. The rotational speed of the turbocompressor rotor is usually in the region of several thousand revolutions per minute, with the process gas flowing around the blades.

If the process gas is contaminated with the particles, the particles impinge on the material of the rotor body in particular in the region of the leading edges of the blades. The degree of hardness of the particles is generally higher than that of the material of the rotor body, and therefore the impingement of the particles on the rotor body entails wear to the rotor body material. These wear tracks caused on the rotor body can damage the turbocompressor rotor in such a manner that both the fluidic effectiveness and the mechanical strength of the turbocompressor rotor are impaired significantly.

A remedy is provided by the provision of sieves, filters or centrifugal separators upstream of the turbocompressor, as a result of which the particles are eliminated from the process gas before the process gas enters into the turbocompressor. These apparatuses are expensive to procure and lead to an energetically unfavorable pressure loss in the process gas flow. If a filter fails, for example because the filter has become full owing to a high quantity of particles, the turbocompressor rotor is nevertheless exposed to high particle loading, wherefrom deep wear tracks can form on the turbocompressor rotor.

A further remedy could be provided, for example, by coating the blades with a hard material. Since this coating is exposed to the particle loading, the coating itself becomes worn. In this respect, the base material of the blade stays protected by the coating only until the coating has been removed by the particles. In addition, sites of the coating which have been removed completely by the particles can be infiltrated by the process gas flow, causing damaging lifting of the coating. The protection of the blades with the coating can therefore be only temporary.

EP 1 215 366 A2 discloses a turbomachine blade which is produced by cutting machining from a primary material. Here, use is made of a steel alloy having a carbon proportion of 0.1% to 0.35% by weight, preferably of 0.15% to 0.3% by weight, and a chromium proportion of 8% to 22% by weight, preferably 9% to 16% by weight.

GB 1 230 536 A discloses a turbine blade for a condensation turbine. In the outer region, this is made of a steel alloy having a chromium proportion of 10% to 15% by weight and a carbon proportion of at least 0.15% by weight.

JP 2000 356103 A, GB 616 432 A, EP 0 867 522 A2, JP 2001 049398 A, JP 5 163 556 A, JP 2 101143 A and EP 0 639 691 A1 likewise disclose turbine blades made of steel alloys. These, too, contain chromium and carbon, with the proportions by weight lying approximately in the range described above.

SUMMARY OF INVENTION

It is an object to provide a turbocompressor rotor and a process for producing the turbocompressor rotor, in which the turbocompressor rotor has a high wear resistance and also can be produced cost-effectively.

The object is achieved by the features of the independent patent claims. Advantageous configurations in this respect are indicated in the further patent claims.

The turbocompressor rotor according to the invention for a turbocompressor for compressing process gas has a rotor body which makes contact with the process gas and which is produced entirely from a stainless steel material comprising 0.3 to 1.2% carbon and 12 to 19% chromium. Here, the steel material comprises the alloy X39CrMo17-1.

The stainless steel material is to be understood as meaning “stainless steels” in accordance with DIN EN 10027-2, table 1, group of the “chemically resistant steels”.

The steel material preferably comprises up to 2.5% molybdenum. Here, it is preferable that the steel material comprises up to 1.5% vanadium.

Alternatively, the turbocompressor rotor according to the invention has a rotor body which makes contact with the process gas and which is produced entirely from a martensitic stainless steel material comprising 0.5 to 1.3% carbon and 26 to 30% chromium.

The steel material preferably comprises up to 2.5% molybdenum.

As a further alternative, the turbocompressor rotor according to the invention has a rotor body which makes contact with the process gas and which is produced entirely from an austenitic-ferritic stainless steel material comprising 0.3 to 0.53% carbon, 26 to 30% chromium and 3 to 6% nickel.

It is preferable that the steel material comprises up to 2.5% molybdenum. The steel material preferably comprises the alloy GX40CrNiMo27-5.

The process according to the invention for producing the turbocompressor rotor comprises the following steps: manufacturing a casting model corresponding to the geometry of the rotor body by rapid technology and producing a casting mold using the casting model, or manufacturing a casting mold corresponding to the negative geometry of the rotor body by rapid technology; introducing the liquid steel material into the casting mold to form a cast workpiece as the rotor body; finishing the turbocompressor rotor with the rotor body.

It is preferable that the rapid technology is a rapid prototyping process.

The steel materials specified according to the invention have a degree of hardness which is comparable to or higher than the degree of hardness of particles which conventionally arise in the process gas. Accordingly, the tendency of the rotor body to erode by abrasive wear caused by the particles is low.

Since the rotor body is produced entirely using the steel material produced according to the invention, its insensitivity to abrasive wear is permanent, since the rotor body manages without, for instance, a protective layer applied to the surface. In addition, the steel materials specified according to the invention are corrosion-resistant, as a result of which the rotor is protected permanently against erosion corrosion.

A casting process is specified as the process according to the invention for producing the turbocompressor rotor. This is advantageous for shaping the steel materials specified according to the invention, since these have a high degree of hardness and as a result can only be machined with difficulty, for example by cutting or by forging. Since the steel materials specified according to the invention are stainless cast steels having a high carbon content, they are advantageously castable.

The rapid technology is provided according to the invention for manufacturing the casting model corresponding to the geometry of the rotor body. To produce the casting mold, the casting model is surrounded with molding sand, with the casting mold being removed from the molding sand after the molding sand has hardened. Alternatively, the casting mold can be produced without the casting model, if the casting mold is produced corresponding to the negative geometry of the rotor body by rapid technology. On account of the use of rapid technology, highly diverse and varying geometries are conceivable both for the casting mold and for the casting model.

In terms of the multitude of variants of the conventional rotor body geometry, it is advantageous to use rapid technology. A wooden model which is conventionally used and complicated to produce can thereby be dispensed with, since the casting model according to the invention can be used instead.

It is preferable that a model of the rotor body made of laser-cured resin is applied in layers by rapid prototyping until the casting model is produced. Alternatively, a laser-hardening molding sand is used for producing the casting mold, with the negative geometry of the rotor body being created in layers in a molding box until the casting mold is produced.

The layered application in the rapid prototyping advantageously has the effect that even complex geometries of rotor bodies can be produced simply and cost-effectively. By way of example, it is possible in a relatively unproblematic manner to produce geometries having overhangs, undercuts, channels, etc. In contrast thereto, similarly complex geometries can be realized only to a limited extent or with a high expenditure by conventional processes, for example milling.

DETAILED DESCRIPTION OF INVENTION

The invention will be explained in more detail hereinbelow with reference to an exemplary embodiment.

A turbocompressor rotor is provided for a turbocompressor for compressing process gas. The turbocompressor rotor has a rotor body, which is in contact with the process gas during operation of the turbocompressor. The turbocompressor rotor is constructed in radial form as an impeller, and therefore the rotor body is formed by a wheel disk, a cover disk spaced apart axially from the wheel disk, and blades which are arranged between the wheel disk and the cover disk and are arranged uniformly in the circumferential direction.

To produce the rotor body, a casting model corresponding to the desired geometry of the rotor body is manufactured. In this process, resin is applied in layers and laser cured by a rapid prototyping process in such a way that the geometry of the rotor body is replicated and the casting model is produced.

The casting model is placed in a molding box and surrounded with hardening molding sand. As soon as the molding sand forms a sufficiently stable casting mold, the casting model is removed and the casting mold formed thereby is filled with a liquid cast steel material. The steel material is the alloy GX40CrNiMo27-5.

As soon as the steel material in the casting mold has cooled and thereby become solid, the cast steel material body obtained is removed from the casting mold and finished as the rotor body by finishing processes. 

1.-5. (canceled)
 6. A turbocompressor rotor for a turbocompressor for compressing process gas, having a rotor body which makes contact with the process gas and which is produced entirely from a stainless steel material comprising 0.3 to 1.2% carbon and 12 to 19% chromium, wherein the steel material comprises the alloy X39CrMo17-1.
 7. The turbocompressor rotor as claimed in claim 6, wherein the steel material comprises up to 2.5% molybdenum.
 8. The turbocompressor rotor as claimed in claim 7, wherein the steel material comprises up to 1.5% vanadium.
 9. A process for producing a turbocompressor rotor as claimed in claim 6 by casting, comprising: manufacturing a casting model corresponding to the geometry of the rotor body by rapid technology and producing a casting mold using the casting model; or manufacturing a casting mold corresponding to the negative geometry of the rotor body by rapid technology; introducing the liquid steel material into the casting mold to form a cast workpiece as the rotor body; finishing the turbocompressor rotor with the rotor body.
 10. The process as claimed in claim 9, wherein the rapid technology is a rapid prototyping process. 